U.S. patent application number 10/609913 was filed with the patent office on 2004-01-22 for x-ray tube rotating anode with an anode body composed of composite fiber material.
This patent application is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Kutschera, Wolfgang.
Application Number | 20040013234 10/609913 |
Document ID | / |
Family ID | 30128068 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040013234 |
Kind Code |
A1 |
Kutschera, Wolfgang |
January 22, 2004 |
X-ray tube rotating anode with an anode body composed of composite
fiber material
Abstract
A rotating anode for an x-ray tube has an anode body having a
target surface with a focal ring, supported by a bearing system.
The anode body is composed of composite fiber material with fibers
exhibiting an especially high heat-conductivity, as well as a high
mechanical strength.
Inventors: |
Kutschera, Wolfgang;
(Aurachtal, DE) |
Correspondence
Address: |
SCHIFF HARDIN & WAITE
6600 SEARS TOWER
233 S WACKER DR
CHICAGO
IL
60606-6473
US
|
Assignee: |
Siemens Aktiengesellschaft
|
Family ID: |
30128068 |
Appl. No.: |
10/609913 |
Filed: |
June 30, 2003 |
Current U.S.
Class: |
378/144 |
Current CPC
Class: |
H01J 2235/1204 20130101;
H01J 2235/1291 20130101; H01J 35/107 20190501 |
Class at
Publication: |
378/144 |
International
Class: |
H01J 035/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2002 |
DE |
10229069.5 |
Claims
I claim as my invention:
1. A rotating anode for an x-ray tube, said rotating anode
comprising: an anode body having a target surface with a focal
ring; a bearing system supporting said anode body; and said anode
body being comprises of composite fiber material having fibers
exhibiting high heat conductivity and high mechanical strength.
2. A rotating anode as claimed in claim 1 wherein said fibers
comprise first fibers having said high heat conductivity and second
fibers having said high mechanical strength.
3. A rotating anode as claimed in claim 2 wherein said first fibers
are oriented in said anode body to rapidly dissipate heat from said
focal ring, and wherein said second fibers are oriented in said
anode body to bear mechanical and thermo-mechanical forces in said
anode body.
4. A rotating anode as claimed in claim 2 wherein said first fibers
are oriented radially in said anode body and wherein said second
fibers are oriented annularly in said anode body.
5. A rotating anode as claimed in claim 2 wherein said bearing
system is a cooled bearing system, and wherein said first fibers
conduct heat from said focal ring to said cooled bearing
system.
6. A rotating anode as claimed in claim 2 wherein said bearing
system is a non-cooled bearing system, and wherein said first
fibers are oriented in said anode body for rapid heat removal from
said anode body without intense heating of said bearing system.
7. A rotating anode as claimed in claim 6 wherein said first fibers
are oriented substantially parallel to said bearing system.
8. A rotating anode as claimed in claim 1 wherein all of said
fibers in said anode body have said high heat conductivity and said
high mechanical strength, and wherein some of said fibers are
oriented radially in said anode body and some of said fibers are
oriented annularly in said anode body.
9. A rotating anode as claimed in claim 1 wherein said anode body
is a formed component.
10. A rotating anode as claimed in claim 1 wherein said anode body
is formed of a shaped fiber mat of said fibers.
11. A rotating anode as claimed in claim 1 wherein said anode body
is a semi-finished fiber mat component.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns a rotating anode for an x-ray
tube with an anode body that has a target surface for incident
electrons with a focal ring, supported by means of a bearing
system.
[0003] 2. Description of the Prior Art
[0004] An X-ray tube with a rotating anode in which the anode plate
is composed of molybdenum alloy is known from Krestel, "Imaging
system for medical diagnostics", page 157f. An x-ray-active cover
layer made of a tungsten-rhenium alloy is deposited on the base
body. A graphite body is mounted under the anode plate for heat
storage, dissipation, and radiation, such that the anode plate has
a soldered interconnection of the Mo and C substrate, in which the
heat spreads out corresponding to the heat conductivity and heat
capacity. The WRe alloy of the cover layer can be 0.6 to 1.6 mm
thick.
[0005] In x-ray tubes, one of the significant technical challenges
is the removal of heat from the focal point and the distribution of
the heat of the focal point over a larger surface by rotating the
anode, which is exposed to large mechanical forces due to the
rotation and thermo-mechanical stresses. Furthermore, the generally
heavyweight of the anode is a disadvantage (in particular for uses
in CT) since high anode weights result in larger stresses of the
rotating anode bearings in CT due to the centrifugal forces
resulting from the rotation of the device.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide a rotating
anode for an x-ray tube of the type described above such that the
high temperature originating in the rotating anode target surface
is more rapidly conducted away than in a conventional focal ring,
so the rotating anode can withstand the thermo-mechanical stresses
for a longer time, or alternatively sustain higher power densities
in a service life of the same length.
[0007] The object is inventively achieved in a rotating anode
wherein the anode body is comprised of composite fiber material
having fibers exhibiting an especially high heat-conductivity, as
well as a high mechanical strength. It is thereby assured that the
heat is dissipated and distributed away from the critical zone in
the focal ring, or conducted to a cooling plate, by utilizing the
very high heat conductivities that CFC materials exhibit, in
particular by the use of as high-modular C-fibers. The temperature
in the focal ring can be lowered by as much as 300 K thereby
minimizing wear and prolonging the service life, depending on the
inventive design, or the applicable short-term capacity of the
x-ray tube can be correspondingly increased.
[0008] It has proven advantageous, to employ first fibers
exhibiting high heat conductivity and second fibers exhibiting high
strength, to orient the direction of the fiber in the anode body so
that the first fibers can quickly dissipate the heat from the path
of the focus and the second fibers absorb the mechanical and
thermo-mechanical forces in the anode body. In accordance with the
invention, for example, the first fibers can be radially formed and
the second fibers can be circularly formed.
[0009] The fibers can exhibit both high heat conductivity and high
strength, with the fibers oriented both radially and
circularly.
[0010] It has proven expedient if the bearing system is cooled, for
the first fibers to conduct the heat from the focal ring away to
the bearing system.
[0011] The poor heat-conductivity transverse to the direction of
the fibers can be advantageously used to keep heat away from
non-cooled and therefore heat-sensitive ball bearings, if the
bearing system is non-cooled and the first fibers are aligned such
that a rapid heat removal from the path of the focus is enabled,
but an intense heating of the bearing system is prevented, for
which purpose the first fibers can be aligned primarily parallel to
the bearing system.
[0012] The anode body can also inventively be fashioned as a formed
component from shaped fiber mat (possibly already shaped as
prepreg) or from a fiber mat semi-finished part.
DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a sectional view of rotating anode in accordance
with the invention with cooled plain bearing system.
[0014] FIG. 2 is a sectional view of rotating anode in accordance
with the invention with cooled ball bearing system.
[0015] FIG. 3 is a sectional view of rotating anode in accordance
with the invention with non-cooled ball bearing system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] An inventive rotating anode is shown in FIG. 1 with an
internally cooled plain bearing system 1, with an anode body 3
mounted at the external rotor 2 of the plain bearing system 1. This
anode body 3 is comprised of a composite fiber material, for
example a carbon fiber composite material, that contains fibers 4
with especially high heat-conductivity that are radially oriented
such that they dissipate the heat from a path 5 of the focal point
mounted in the external region of a rotating anode top down on a
bracket to the cooled sliding support system. The path 5 of the
focal point is fashioned by plating the anode body with heavy
metals, or can be formed by a soldered-on heavy metal ring.
Furthermore, the anode body 3 is provided with reinforcing fibers 6
with especially high mechanical strength that, for example, can be
annularly arranged. These reinforcing fibers 6 can be distributed
over the entire anode body 3 or, as is shown in FIG. 1, can be
present only in the external regions that are exposed to especially
high centrifugal forces. In this case, the anode body 3 is
fashioned as a formed component having the desired shape.
[0017] A further exemplary embodiment of an inventive rotating
anode is shown in FIG. 2 that has an internally-cooled ball bearing
system 7. Again, the anode body 3 made from a composite fiber
material with the heat-conducting fibers 4 and reinforcing fibers 6
is affixed to the rotor 8 of the internally cooled ball bearing
system 7. The externally located oblique straight surface of the
path 5 of the focal point is again plated with heavy metal, or can
be a soldered-on heavy metal ring. In the exemplary embodiment
according to FIG. 2, the anode body 3 is fabricated from shaped
fiber mat (possibly already shaped as prepreg).
[0018] A further exemplary embodiment of a rotating anode with a
non-cooled ball bearing system 9 is shown in FIG. 3. Mounted on the
axis 10 of the ball bearing system 9 is the anode body 3 that is
again comprised of composite fiber material and provided with
heat-conducting and reinforcing fibers 4 and 6. The annular path 5
of the focal point (that is arranged at the necessary angle to
properly emit x-rays) is again provided in the external region. In
this exemplary embodiment, the anode body 3 is fabricated from an
appropriate fiber-mat semi-finished part.
[0019] The heat conducting fibers 4 are arranged vertically,
differently than in the cooled versions, i.e. parallel to the axis
10, such that a rapid removal of heat from the focal point is
enabled but an intense heating of the bearing system 9 is
prevented.
[0020] Throughout the inventive embodiment of the anode body 3, the
supporting structure of this rotating anode is comprised of
composite fiber material that has fibers with especially high
heat-conductivity, as well as fibers (the same or another type)
with a high mechanical strength.
[0021] The direction of the fibers in the supporting anode
structure is selected such that the fibers with high
heat-conductivity can rapidly dissipate the heat from the path of
the focus, and the fibers with high strength transfer the
mechanical and thermo-mechanical forces to the supporting
structure.
[0022] The configuration of the fibers with high heat-conductivity
also can be oriented such that they conduct the heat from the path
of the focus to a heat sink (for example, a cooled bearing system).
Alternatively, they can be purposefully oriented such that,
although a rapid heat dissipation ensues from the path of the
focus, the poor heat conductivity transverse to the fiber
orientation is used in order to keep heat away from ball bearing
systems (for example, those that are non-cooled and therefore
heat-sensitive).
[0023] A carbon composite fiber material or a composite material of
high-modular fibers, with heat-conductivity in the direction of the
fibers of a magnitude comparable to the heat-conductivity of
copper, are suitable as the anode material.
[0024] One advantage of the inventive anode composition is good
heat dissipation away from the focal point allowed by high
capacities. CFC achieve in the direction of fiber up to 10-fold
higher heat-conductivity as super-pure graphite or Mo. Given
consistent heat records, FE-calculations show up to 300K lower
focal ring temperatures than conventional anodes.
[0025] A further advantage is high strength with lower weight.
Conventional Mo anodes for the CT application have a
strength/thickness ratio of 78 MPa/g/cm.sup.3; graphite anodes, as
they are sometimes used, have a ratio of 21 MPa/g/cm.sup.3; fiber
composite materials such as, for example, CFC achieve up to 270
MPa/g/cm.sup.3, meaning that a higher anode rotation frequency is
achievable, in particular higher rotation frequencies than with
graphite anodes. At the same time, the layer stress due to its own
weight and centrifugal forces in the CT gantry is not larger than
with graphite anodes, and significantly smaller than for
conventional Mo-C anodes.
[0026] Although modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventor to embody
within the patent warranted hereon all changes and modifications as
reasonably and properly come within the scope of his contribution
to the art.
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